GB1563451A - Nitro-substituted polyaromatic polycarboxylic acid compositions and processes for their preparation from coal based materials - Google Patents

Description

(54) NITRO-SUBSTITUTED POLYAROMATIC POLYCARBOXYLIC ACID COMPOSITIONS AND PROCESSES FOR THEIR PREPARATION FROM COAL BASED MATERIALS (71) We, GULF RESEARCH & DEVELOPMENT COMPANY, a corporation organised and existing under the laws of the state of Delaware, U.S.A., of P.O. Box 2038, Pittsburgh, Pennsylvania 15230, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to polyaromatic polycarboxylic acids and to a method of preparing same.

Treating a carbonaceous material, such as coal, with nitric acid to obtain carboxylic acids is shown in U.S. Patents Nos. 2,555,410 to Howard, 2,726,262 to Grosskinsky et al. 2,949,350 to Heinze et al, 2,991,189 to Rickert and 3,173,947 to Benning et al. In each of these processes the acids obtained are said to be water soluble. Creigton et al in U.S. Patent No. 3,468,943 are interested in passing coal through a screw conveyor and at spaced apart intervals feeding appropriate quantities of concentrated nitric acid so that it is completely reacted with the coal before the coal arrives at the next nitric feed point to obtain humic acids which are said to be partially soluble in sodium hydroxide solution but substantially insoluble in water.

According to the present invention there is provided a process for converting coal to a mixture of polycyclic aromatic polycarboxylic acids carrying nuclear nitro groups that is substantially soluble in polar solvent but insoluble in water comprising reacting a slurry containing coal with aqueous nitric acid, separating a solids fraction from the reaction product, extracting the solids fraction with a polar solvent and then removing the solvent from the extract to obtain the desired carboxylic acid mixture. The individual components of said acid mixtures are believed to be composed of condensed and/or non-condensed benzene rings, with an average number of benzene rings in the individual molecules ranging from two to ten, but generally from three to eight. On the average, the number of carboxyl groups carried by the individual molecules ranges from four to ten, generally from six to eight, and the average number of nitro groups from one to four, generally from two to three. The average molecular weight of the mixture ranges from 600 to 1500, generally from 700 to 1000, and the average neutral equivalent ranges from 80 to 200, generally from 100 to 150. A typical analysis of the novel mixture is defined below in Table I in approximate amounts.

TABLE I Weight Per Cent Broad Range Preferred Range Carbon 50 to 60 52 to 56 Hydrogen 3 to 5 3.7 to 4.4 Nitrogen 3 to 6 4 to 5 Oxygen 25 to 45 30 to 40 Sulfur 0.2 to 0.5 0.3 to 0.5 Ash 0.1 two5 0.3to3 A preferred and novel procedure for obtaining the above novel mixtures is described in reference to the Figure. There is introduced into reactor 2 by line 4 an aqueous solution of nitric acid and by line 6 the coal (carbonaceous material). The nitric acid can have a concentration of from five to 90 per cent, but preferably will be in the range of from 10 to 70 per cent. The carbonaceous material is preferably a solid in the form of a slurry, for example, an aqueous slurry containing the carbonaceous material in particulate form and from 50 to 90 weight per cent of water.

The solid carbonaceous material that can be used herein can have the following composition on a moisture-free basis: TABLE II Weight Per Cent Broad Range Preferred Range Carbon 45-95 6092 Hydrogen 2.57 46 Oxygen 2.045 3-25 Nitrogen 0.75-2.5 0.75-2.5 Sulfur 0.3-10 0.5-6 The carbon and hydrogen content of the carbonaceous material resides primarily in multi-ring aromatic compounds (condensed and/or uncondensed) and heterocyclic compounds. Oxygen and nitrogen are believed to be present primarily in chemical combination but not necessarily with each other. Some of the sulfur is believed to be present in chemical combination with the aromatic compounds and some in chemical combination with inorganic elements associated therewith, for example, iron and calcium.

In addition to the above elements, the solid carbonaceous material being treated herein will also contain solid, primarily inorganic, compounds which will not be converted to the desired organic mixture claimed herein, which are termed ash, and are composed chiefly of compounds of silicon, aluminum, iron and calcium, with smaller amounts of compounds of magnesium, titanium, sodium and potassium. The ash content of the carbonaceous material treated herein will amount to less than 50 weight per cent, based on the moisture-free carbonaceous material, but, in general, will amount to from 0.1 to 30 weight per cent, usually from 0.5 to 20 weight per cent.

Anthracitic, bituminous and subbituminous coal, lignitic materials, and other type of coal products referred to in ASTM D-388 are exemplary of the solid carbonaceous materials which can be treated in accordance with the process defined herein to produce the claimed organic mixture. Some of these carbonaceous materials in their raw state will contain relatively large amounts of water. These can be dried prior to use herein. The carbonaceous material, prior to use. is preferably ground in a suitable attrition machine, such as a hammermill, to a size such that at least 50 per cent of the carbonaceous material will pass through a 40-mesh (U.S. Series) sieve. As noted, the carbonaceous material is slurried in a suitable carrier, preferably water, prior to reaction with nitric acid. If desired, the carbonaceous material can be treated, prior to reaction herein, using any conventional means, to remove therefrom any materials forming apart thereof that will not be converted in reaction with nitric acid herein.

The reactant mixture in reactor 2 is stirred while being maintained at a temperature of from 15 to 2000C., preferably from SOC to 1000C., and a pressure of from atmospheric to 1000 pounds per square inch gauge (from atmospheric to 70 kilograms per square centimeter), preferably from atmospheric to 500 pounds per square inch gauge (from atmospheric to 35 kilograms per square centimeter) for from 0.5 to 15 hours, preferably from two to six hours. In order to obtain the desired mixture herein without losing appreciable amounts of carboxyl and/or nitro groups on the acids that are formed during the oxidation, and to obtain the desired acids in high yields in reactor 2, it is desirable that the reaction conditions therein, namely nitric acid concentration, temperature, pressure and reaction time, be so correlated to minimize and, preferably, to avoid decarboxylation and denitrification. Gaseous products, such as nitrogen oxides, can be removed from reaction 2 by line 8.

The reaction product is removed from reactor 2 by line 10. We have found that the reaction product is soluble in, or reacts with, sodium hydroxide. At this point it is necessary to separate the oxidized product from the water and nitric acid associated therewith. This separation must be accomplished in a manner such that the carboxyl and nitro groups are not removed from the acid product. Distillation for the removal of water will not suffice, because under the conditions required for such separation, a significant loss of carboxyl groups and nitro groups occurs.

Accordingly, we have found that a mechanical separation suffices. The reaction product in line 10 is therefore led to a separator 12, which can be, for example, a filter or a centrifuge.

The solids that are recovered in separator 12, also soluble in sodium hydroxide, are led by line 14 to a separator 16 wherein they are subjected to extraction with acetone that is introduced therein by line 18. Such separation can be carried out at a temperature of from 200 to 60"C., preferably from 250 to 500 C., and a pressure of from atmospheric to 500 pounds per square inch gauge (from atmospheric to 35 kilograms per square centimeter), preferably from atmospheric to 100 pounds per square inch gauge (from atmospheric to seven kilograms per square centimeter). The solid material, acetone-insoluble water-insoluble polyaromatic polycarboxylic acids, is removed from separator 16 by line 20 and the acetone solution of the novel acid mixture by line 22. The acetone solution is then led to drier 24 wherein acetone is separated therefrom by line 26 and the desired novel acetone-soluble, water-insoluble polyaromatic, polycarboxylic acid mixture claimed herein is recovered in line 28. As before, the acid mixture in drier 24 may be treated by so correlating the conditions therein to remove acetone therefrom in such manner so as to minimize and, preferably, avoid, decarboxylation and denitrification. The temperature can be in the range of from 10 to 600C., preferably from 2UO to 500C., the pressure from 10 millimeters of mercury to atmospheric, preferably from 30 millimeters of mercury to atmospheric, for from 0.5 to 24 hours, preferably from one to five hours.

The filtrate obtained in separator 12 is removed therefrom by line 30. In all cases the filtrate will contain water, nitric acid and most of the inorganic material (ash) that was present in the carbonaceous charge. In addition there can also be present other oxidized material, which are primarily acetone-soluble, waterinsoluble organic acids.

Separation of the filtrate into its component parts can be effected as follows. It can be passed to distillation tower 32 maintained at a temperature of from 500 to 100 C., preferably from 70" to 900 C. and a pressure of from 10 millimeters of mercury to atmospheric, preferably from 30 millimeters of mercury to atmospheric. Under these conditions nitric acid and water are removed from distillation tower 32 by line 34 and solids by line 36. The solids are led to separator 38 where they are subjected to extraction with acetone introduced therein by line 40. The conditions in separator 38 are similar to those used in separator 16. A mixture of acetone-soluble, water-soluble monoaromatic polycarboxylic acids is removed from separator 38 by line 42 and substantially all of the inorganic material that was present in the carbonaceous charge by line 44.

Several runs were carried out in which a North Dakota Lignite analyzing as follows, on a substantially moisture-free basis, was subjected to oxidation using nitric acid as the oxidant: 65.03 weight per cent carbon, 4.0 weight per cent hydrogen, 27.0 weight per cent oxygen, 0.92 weight per cent sulfur, 0.42 weight per cent nitrogen and 0.04 weight per cent ash. The ash was further analyzed and found to contain 43 weight per cent oxygen, 7.8 weight per cent sulfur and the remainder metals. In each of Runs Nos. 3 to 8, the data of which are summarized below in Table III, 70 per cent aqueous nitric acid was used. In Runs Nos. 1 and 2, the aqueous nitric acid used had a concentration of 90 per cent. In Runs Nos. 4 to 8. over a period of two hours, 100 milliliters of the defined nitric acid was gradually added to the stirred slurry containing 100 grams of powdered lignite defined above (corresponding to 67.5 grams of moisture-free feed) and 370 grams of water while maintaining the contents at selected temperature levels and atmospheric pressure.

In Run No. 3, otherwise identical to Runs Nos. 4 to 8, a five-hour reaction time was employed. In the remaining runs solid lignite was added gradually to 411 milliliters of nitric acid at a rate sufficient to maintain the reaction temperature. Nitrogen oxides were permitted to escape from the reaction zone as they evolved.

At the end of the reaction period the product slurry was withdrawn from the reaction zone and filtered to obtain a solids fraction and a filtrate. The solids were extracted with acetone at atmospheric temperature and pressure. The acetone solution was then subjected to evaporation at atmospheric temperature and pressure to obtain the novel mixture herein. The acetone insoluble portion was found to be soluble in sodium hydroxide and to comprise organic acids of a relatively higher molecular weight than the acetone-soluble portion.

The filtrate in Runs Nos. 7 and 8 was found to consist essentially of unreacted nitric acid, water and inorganic materials (ash). However, in each of Runs Nos. I to 6 some acetone soluble, water-insoluble organic acids were also found. The workup of the filtrate was carried out as follows. Initially the filtrate was subjected to distillation to separate unreacted nitric acid and water therefrom. The remaining solids were subjected to extraction with acetone at atmospheric temperature and atmospheric pressure. The acetone solution was dried to remove acetone therefrom, resulting in the recovery of small amounts of the acetone-soluble, water-insoluble organic acids substantially completely soluble in sodium hydroxide. The average molecular weight of the mixtures obtained was 800 and the average neutral equivalent 110. The residue was mainly ash. The data obtained are summarized below in Table III.

TABLE III Reaction Acetone-Soluble, Run Temerature, Time, Water-Isoluble Analysis of Product, Weight Per Cent No. C. Hours Product, Grams Carbon Hydroegn Nitrogen Oxygen Sulfur Ash 1 15 2 85.6 48.03 3.33 4.53 41.06 0.24 2.81 2 30 2 71.4 48.03 3.57 5.10 40.63 0.19 2.48 3 50 5 67.0 56.30 4.80 4.60 33.27 0.31 0.72 4 70 2 51.1 55.52 3.72 4.70 35.13 0.30 0.63 5 90 2 52.5 53.94 4.38 4.61 36.39 0.25 0.43 6 110 2 35.5 54.53 4.36 4.51 35.35 0.27 0.98 7 130 2 7.1 56.8 4.20 4.31 33.59 0.24 0.86 8 150 2 4.7 61.65 5.06 4.03 27.95 0.26 1.05 Note from the above table that while an acetone-soluble water-insoluble material was obtained in each of the runs, the largest amount was obtained at the lower temperatures.

Although we have stated above that the novel composition is acetone-soluble and we have shown the use of acetone as suitable in the process defined herein, this has been done merely as a characterization of the composition and to exemplify one embodiment of our process. Many polar solvents can be used in place of acetone herein. Among the polar solvents that have been used are methanol, ethanol, isopropanol, methyl ethyl ketone, tetrahydrofuran, dioxane and cyclohexanone.

Since the novel mixture claimed herein has abundant functionality in both carboxyl and nitro groups, it is apparent that the mixture lends itself to many known chemical reactions, for example, esterification of the carboxyl groups and hydrogenation of the nitro groups to amines. We have found that the novel mixtures defined herein are effective blowing agents for the purpose of incorporating the same in well-known resins, such as polyethylene, to increase permanently the volume of the resin.

Claims (11)

WHAT WE CLAIM IS:

1. A process for converting coal to a mixture of polycyclic aromatic polycarboxylic acids carrying nuclear nitro groups that is substantially soluble in polar solvent but insoluble in water comprising reacting a slurry containing coal with aqueous nitric acid, separating a solids fraction from the reaction product, extracting the solids fraction with a polar solvent and then removing the solvent from the extract to obtain the desired carboxylic acid mixture.

2. A process according to claim 1, wherein said polar solvent is acetone.

3. A process according to claim I or claim 2, wherein the nitric acid has a concentration of from 5 to 90 per cent and the reaction is carried out at a temperature of from 15C to 2000C for a period of from 0.5 to 15 hours.

4. A process according to claim 3, wherein the nitric acid has a concentration of from 10 to 70 per cent and the reaction is carried out at a temperature of from 50" to 1000C for a period of from two to six hours.

5. A process according to any of claims 1 to 4, wherein the solids fraction is separated by filtration.

6. A process according to any of claims 1 to 5 wherein the solvent is removed from the extract by evaporation.

7. A process according to any of claims 1 to 6, wherein the coal is lignite.

8. A process according to any of claims 1 to 7, in which a liquid fraction is recovered from the reaction product, said liquid fraction is heated to distil off water and unreacted nitric acid and to obtain a solid fraction, the solid fraction being recovered, extracted with solvent and a product comprising solvent-soluble, water-soluble monoaromatic polycarboxylic acids is recovered from the extract.

9. A process according to any of claims 1 to 8, in which solid material remaining after solvent extraction of the reaction product is recovered as a product comprising solvent-insoluble water-insoluble polyaromatic polycarboxylic acids.

10. A process according to claim 1, substantially as hereinbefore described.

11. Each of the products of the process claimed in any one of claims 1 to 10.